Michael Fellinger - Academia.edu (original) (raw)

Papers by Michael Fellinger

Research paper thumbnail of Thermal transport across high-pressure semiconductor-metal transition in Si andSi0.991Ge0.009

Physical Review B, 2015

Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the ... more Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the diamond anvil cell (DAC) and provide non-contact measurements of thermal transport properties. We have performed regular and beam-offset TDTR to establish the thermal conductivities of Si and Si 0.991 Ge 0.009 across the semiconductor-metal phase transition and up to 45 GPa. The thermal conductivities of metallic Si and Si(Ge) are comparable to aluminum and indicative of predominantly electronic heat carriers. Metallic Si and Si(Ge) have an anisotropy of approximately 1.4, similar to that of beryllium, due to the primitive hexagonal crystal structure. We used the Wiedemann-Franz law to derive the associated electrical resistivity, and found it consistent with the Bloch-Grüneisen model.

Research paper thumbnail of Solutes that reduce yield strength anisotropies in magnesium from first principles

Physical Review Materials, 2022

Using Labusch-type solid solution strengthening models parameterized with DFT-computed solute-dis... more Using Labusch-type solid solution strengthening models parameterized with DFT-computed solute-dislocation interaction energies, we perform a computational search for 63 solutes across the periodic table to find those that lower anisotropy ratios (non-basal to basal CRSS) of magnesium potentially increasing its ductility per the von Mises criterion. For this purpose, we compute changes in strength for solutes as a function of composition and temperature, and compute anisotropy ratios for solutes that include both rare earth and non-rare earth elements. We specifically focus on solute-dislocation interaction energies in the following DFT-optimized dislocations as representative of three non-basal plastic deformation modes: c + a edge, (1012) tension twinning edge, and the (1011) compression twinning edge. We find that solute-induced changes in non-basal deformation modes can be approximated using a second-order polynomial in the size misfit of the solutes, which permits rapid screening of solutes. Our approach to identify solutes known to improve strengthening incorporates solute solubility, and suggests other solutes that not have been previously explored for strengthening. The 8 rare-earth solutes that our method suggests as the best, ordered by increasing anisotropy ratios at their optimal concentrations, are: Gd, Tb, Dy, Nd, Ho, Er, Tm, and Yb. The 12 non-rare-earth solutes that our method suggests as the best, ordered by increasing anisotropy ratios, are: Y,

Research paper thumbnail of MEAM Potential for Mo developed by Park et al. (2012) v001

Density-functional theory (DFT) energies, forces, and elastic constants determine the parametriza... more Density-functional theory (DFT) energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method (MEAM) potential for molybdenum. The accuracy and transferability of the potential are verified by comparison to experimental and DFT data for point defects, phonons, thermal expansion, surface and stacking fault energies, and ideal shear strength. Searching the energy landscape predicted by the potential using a genetic algorithm verifies that it reproduces not only the correct bcc ground state of molybdenum but also all low-energy metastable phases. The potential is also applicable to the study of plastic deformation and used to compute energies, core structures, and Peierls stresses of screw and edge dislocations.

Research paper thumbnail of MEAM Potential for Ta developed by Park et al. (2012) v001

Density-functional theory energies, forces, and elastic constants determine the parametrization o... more Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for tantalum.

Research paper thumbnail of MEAM Potential for W developed by Park et al. (2012) v001

Density-functional theory energies, forces, and elastic constants determine the parametrization o... more Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for tungsten.

Research paper thumbnail of Impact of solutes on the lattice parameters and elastic stiffness coefficients of hcp Fe from first-principles calculations

Computational Materials Science

The hexagonal close-packed (hcp)-martensite phase in steels nucleates from the-austenite parent p... more The hexagonal close-packed (hcp)-martensite phase in steels nucleates from the-austenite parent phase and can undergo further transformation to the-martensite phase or exist as a metastable phase depending on temperature, mechanical loading, and alloy chemistry. The solute-dependent lattice parameters and elastic stiffness coefficients C ij of hcp Fe influence the mechanical properties of steels containing the-martensite phase, as well as the martensitic transformations between the phases. We use density functional theory to calculate the lattice parameters and C ij of single-crystal hcp Fe as functions of solute concentration in the dilute limit for the substitutional solutes Al, B, Cu, Mn, and Si, and the octahedral interstitial solutes C and N. Our computationally efficient methodology separates the solute dependence of the C ij into lattice strain and chemical bonding contributions. The computed data can be used to estimate the effect of solutes on polycrystalline elastic moduli and the strain energy associated with martensitic transformations. The data can also serve as inputs to microstructure-based models of multiphase steels containing the-martensite phase.

Research paper thumbnail of Geometries of edge and mixed dislocations in bcc Fe from first-principles calculations

Physical Review Materials

We use density functional theory (DFT) to compute the core structures of a 0 [100](010) edge, a 0... more We use density functional theory (DFT) to compute the core structures of a 0 [100](010) edge, a 0 [100](011) edge, a 0 /2[111](110) edge, and a 0 /2[111](110) 71 • mixed dislocations in body-centered cubic (bcc) Fe. The calculations are performed using flexible boundary conditions (FBC), which effectively allow the dislocations to relax as isolated defects by coupling the DFT core to an infinite harmonic lattice through the lattice Green function (LGF). We use the LGFs of the dislocated geometries in contrast to most previous FBC-based dislocation calculations that use the LGF of the bulk crystal. The dislocation LGFs account for changes in the topology of the crystal in the core as well as local strain throughout the crystal lattice. A simple bulk-like approximation for the force constants in a dislocated geometry leads to dislocation LGFs that optimize the core structures of the a 0 [100](010) edge, a 0 [100](011) edge, and a 0 /2[111](110) 71 • mixed dislocations. This approximation fails for the a 0 /2[111](110) dislocation however, so in this case we derive the LGF from more accurate force constants computed using a Gaussian approximation potential. The standard deviations of the dislocation Nye tensor distributions quantify the widths of the dislocation cores. The relaxed cores are compact, and the local magnetic moments on the Fe atoms closely follow the volumetric strain distributions in the cores. We also compute the core structures of these dislocations using eight different classical interatomic potentials, and quantify symmetry differences between the cores using the Fourier coefficients of their Nye tensor distributions. Most of the core structures computed using the classical potentials agree well with the DFT results. The DFT core geometries provide benchmarking for classical potential studies of work-hardening, as well as substitutional and interstitial sites for computing solute-dislocation interactions that serve as inputs for mesoscale models of solute strengthening and solute diffusion near dislocations.

Research paper thumbnail of Data files for ab initio calculations of the lattice parameter and elastic stiffness coefficients of bcc Fe with solutes

Data in brief, 2017

We present computed datasets on changes in the lattice parameter and elastic stiffness coefficien... more We present computed datasets on changes in the lattice parameter and elastic stiffness coefficients of bcc Fe due to substitutional Al, B, Cu, Mn, and Si solutes, and octahedral interstitial C and N solutes. The data is calculated using the methodology based on density functional theory (DFT) presented in Ref. (M.R. Fellinger, L.G. Hector Jr., D.R. Trinkle, 2017) [1]. All the DFT calculations were performed using the Vienna Ab initio Simulations Package (VASP) (G. Kresse, J. Furthmüller, 1996) [2]. The data is stored in the NIST dSpace repository (http://hdl.handle.net/11256/671).

Research paper thumbnail of Ti-V alloy phase diagram: DFT-based cluster approach

Bulletin of the American Physical Society, Mar 7, 2007

Research paper thumbnail of Ab initio-based interatomic potentials for body-centered cubic refractory metals

A fundamental understanding of transformation and deformation processes in the bcc refractory met... more A fundamental understanding of transformation and deformation processes in the bcc refractory metals (V, Nb, Ta, Mo, and W) is vital for designing new bcc-based commercial alloys with desired properties. Such an understanding is aided by computational methods capable of reaching length and time scales needed for meaningful simulations of phase transformations and extended defects responsible for plastic deformation. Classical interatomic potentials are indispensable for simulating such phenomena inaccessible to first-principles methods. We develop accurate and robust modified embedded-atom method (MEAM) potentials [1, 2] for the bcc metals by fitting the model parameters to accurate first-principles data. The potentials are applicable for studying mechanical and thermodynamic properties, yielding excellent agreement with both experiments and first-principles calculations. Supported by DOE-Basic Energy Sciences, Division of Materials Sciences (DE-FG02-99ER45795). Computational resources provided by OSC and NERSC.

Research paper thumbnail of Embedded-atom method potential for niobium

Aps Meeting Abstracts, Mar 1, 2010

Research paper thumbnail of Development of an Embedded-Atom Method Potential for Niobium

Aps Meeting Abstracts, Mar 1, 2009

Research paper thumbnail of Embedded Atom Method Potential for Titanium-Vanadium Alloys

Aps Meeting Abstracts, Mar 1, 2008

Research paper thumbnail of Force-matched embedded-atom method potential for niobium

Physical Review B, 2010

Large-scale simulations of plastic deformation and phase transformations in alloys require reliab... more Large-scale simulations of plastic deformation and phase transformations in alloys require reliable classical interatomic potentials. We construct an embedded-atom method potential for niobium as the first step in alloy potential development. Optimization of the potential parameters to a wellconverged set of density-functional theory (DFT) forces, energies, and stresses produces a reliable and transferable potential for molecular dynamics simulations. The potential accurately describes properties related to the fitting data, and also produces excellent results for quantities outside the fitting range. Structural and elastic properties, defect energetics, and thermal behavior compare well with DFT results and experimental data, e.g., DFT surface energies are reproduced with less than 4% error, generalized stacking-fault energies differ from DFT values by less than 15%, and the melting temperature is within 2% of the experimental value.

Research paper thumbnail of Grain-boundary free energy via thermodynamic integration

The Journal of Chemical Physics, 2006

In a previous publication by Lusk and Beale [Phys. Rev. E 69, 026117 (2004)], fluctuating cell (F... more In a previous publication by Lusk and Beale [Phys. Rev. E 69, 026117 (2004)], fluctuating cell (FC) theory was used to estimate the free energy of symmetric tilt grain boundaries in an assembly of nearly hard disks. The FC method is much faster than the more traditional thermodynamic integration, but the accuracy of the algorithm has not been assessed in association with persistent defect structures. This motivated the present work wherein the FC free energies are compared directly with the data obtained via thermodynamic integration from an Einstein crystal to an assembly of hard disks. This comparison is made over the range of possible misorientations for symmetric tilt boundaries and indicates that the FC method gives quantitatively accurate estimates for grain-boundary free energy. We also demsonstrate that the FC approximation is quantitatively accurate at determining the free-energy contribution of each particle whether in the bulk or the grain boundary. The FC calculation is about two orders of magnitude faster than a full thermodynamic integration. This approach may offer a numerically efficient means of estimating the free energy of persistent defect structures to greater accuracy than is afforded by the quasiharmonic and local harmonic approximations.

Research paper thumbnail of Ab initio based empirical potential used to study the mechanical properties of molybdenum

Density-functional theory energies, forces, and elastic constants determine the parametrization o... more Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for molybdenum. The accuracy and transferability of the potential are verified by comparison to experimental and density-functional data for point defects, phonons, thermal expansion, surface and stacking fault energies, and ideal shear strength. Searching the energy landscape predicted by the potential using a genetic algorithm verifies that it reproduces not only the correct bcc ground state of molybdenum but also all low-energy metastable phases. The potential is also applicable to the study of plastic deformation and used to compute energies, core structures, and Peierls stresses of screw and edge dislocations.

Research paper thumbnail of Thermal transport across high-pressure semiconductor-metal transition in Si andSi0.991Ge0.009

Physical Review B, 2015

Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the ... more Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the diamond anvil cell (DAC) and provide non-contact measurements of thermal transport properties. We have performed regular and beam-offset TDTR to establish the thermal conductivities of Si and Si 0.991 Ge 0.009 across the semiconductor-metal phase transition and up to 45 GPa. The thermal conductivities of metallic Si and Si(Ge) are comparable to aluminum and indicative of predominantly electronic heat carriers. Metallic Si and Si(Ge) have an anisotropy of approximately 1.4, similar to that of beryllium, due to the primitive hexagonal crystal structure. We used the Wiedemann-Franz law to derive the associated electrical resistivity, and found it consistent with the Bloch-Grüneisen model.

Research paper thumbnail of Solutes that reduce yield strength anisotropies in magnesium from first principles

Physical Review Materials, 2022

Using Labusch-type solid solution strengthening models parameterized with DFT-computed solute-dis... more Using Labusch-type solid solution strengthening models parameterized with DFT-computed solute-dislocation interaction energies, we perform a computational search for 63 solutes across the periodic table to find those that lower anisotropy ratios (non-basal to basal CRSS) of magnesium potentially increasing its ductility per the von Mises criterion. For this purpose, we compute changes in strength for solutes as a function of composition and temperature, and compute anisotropy ratios for solutes that include both rare earth and non-rare earth elements. We specifically focus on solute-dislocation interaction energies in the following DFT-optimized dislocations as representative of three non-basal plastic deformation modes: c + a edge, (1012) tension twinning edge, and the (1011) compression twinning edge. We find that solute-induced changes in non-basal deformation modes can be approximated using a second-order polynomial in the size misfit of the solutes, which permits rapid screening of solutes. Our approach to identify solutes known to improve strengthening incorporates solute solubility, and suggests other solutes that not have been previously explored for strengthening. The 8 rare-earth solutes that our method suggests as the best, ordered by increasing anisotropy ratios at their optimal concentrations, are: Gd, Tb, Dy, Nd, Ho, Er, Tm, and Yb. The 12 non-rare-earth solutes that our method suggests as the best, ordered by increasing anisotropy ratios, are: Y,

Research paper thumbnail of MEAM Potential for Mo developed by Park et al. (2012) v001

Density-functional theory (DFT) energies, forces, and elastic constants determine the parametriza... more Density-functional theory (DFT) energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method (MEAM) potential for molybdenum. The accuracy and transferability of the potential are verified by comparison to experimental and DFT data for point defects, phonons, thermal expansion, surface and stacking fault energies, and ideal shear strength. Searching the energy landscape predicted by the potential using a genetic algorithm verifies that it reproduces not only the correct bcc ground state of molybdenum but also all low-energy metastable phases. The potential is also applicable to the study of plastic deformation and used to compute energies, core structures, and Peierls stresses of screw and edge dislocations.

Research paper thumbnail of MEAM Potential for Ta developed by Park et al. (2012) v001

Density-functional theory energies, forces, and elastic constants determine the parametrization o... more Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for tantalum.

Research paper thumbnail of MEAM Potential for W developed by Park et al. (2012) v001

Density-functional theory energies, forces, and elastic constants determine the parametrization o... more Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for tungsten.

Research paper thumbnail of Impact of solutes on the lattice parameters and elastic stiffness coefficients of hcp Fe from first-principles calculations

Computational Materials Science

The hexagonal close-packed (hcp)-martensite phase in steels nucleates from the-austenite parent p... more The hexagonal close-packed (hcp)-martensite phase in steels nucleates from the-austenite parent phase and can undergo further transformation to the-martensite phase or exist as a metastable phase depending on temperature, mechanical loading, and alloy chemistry. The solute-dependent lattice parameters and elastic stiffness coefficients C ij of hcp Fe influence the mechanical properties of steels containing the-martensite phase, as well as the martensitic transformations between the phases. We use density functional theory to calculate the lattice parameters and C ij of single-crystal hcp Fe as functions of solute concentration in the dilute limit for the substitutional solutes Al, B, Cu, Mn, and Si, and the octahedral interstitial solutes C and N. Our computationally efficient methodology separates the solute dependence of the C ij into lattice strain and chemical bonding contributions. The computed data can be used to estimate the effect of solutes on polycrystalline elastic moduli and the strain energy associated with martensitic transformations. The data can also serve as inputs to microstructure-based models of multiphase steels containing the-martensite phase.

Research paper thumbnail of Geometries of edge and mixed dislocations in bcc Fe from first-principles calculations

Physical Review Materials

We use density functional theory (DFT) to compute the core structures of a 0 [100](010) edge, a 0... more We use density functional theory (DFT) to compute the core structures of a 0 [100](010) edge, a 0 [100](011) edge, a 0 /2[111](110) edge, and a 0 /2[111](110) 71 • mixed dislocations in body-centered cubic (bcc) Fe. The calculations are performed using flexible boundary conditions (FBC), which effectively allow the dislocations to relax as isolated defects by coupling the DFT core to an infinite harmonic lattice through the lattice Green function (LGF). We use the LGFs of the dislocated geometries in contrast to most previous FBC-based dislocation calculations that use the LGF of the bulk crystal. The dislocation LGFs account for changes in the topology of the crystal in the core as well as local strain throughout the crystal lattice. A simple bulk-like approximation for the force constants in a dislocated geometry leads to dislocation LGFs that optimize the core structures of the a 0 [100](010) edge, a 0 [100](011) edge, and a 0 /2[111](110) 71 • mixed dislocations. This approximation fails for the a 0 /2[111](110) dislocation however, so in this case we derive the LGF from more accurate force constants computed using a Gaussian approximation potential. The standard deviations of the dislocation Nye tensor distributions quantify the widths of the dislocation cores. The relaxed cores are compact, and the local magnetic moments on the Fe atoms closely follow the volumetric strain distributions in the cores. We also compute the core structures of these dislocations using eight different classical interatomic potentials, and quantify symmetry differences between the cores using the Fourier coefficients of their Nye tensor distributions. Most of the core structures computed using the classical potentials agree well with the DFT results. The DFT core geometries provide benchmarking for classical potential studies of work-hardening, as well as substitutional and interstitial sites for computing solute-dislocation interactions that serve as inputs for mesoscale models of solute strengthening and solute diffusion near dislocations.

Research paper thumbnail of Data files for ab initio calculations of the lattice parameter and elastic stiffness coefficients of bcc Fe with solutes

Data in brief, 2017

We present computed datasets on changes in the lattice parameter and elastic stiffness coefficien... more We present computed datasets on changes in the lattice parameter and elastic stiffness coefficients of bcc Fe due to substitutional Al, B, Cu, Mn, and Si solutes, and octahedral interstitial C and N solutes. The data is calculated using the methodology based on density functional theory (DFT) presented in Ref. (M.R. Fellinger, L.G. Hector Jr., D.R. Trinkle, 2017) [1]. All the DFT calculations were performed using the Vienna Ab initio Simulations Package (VASP) (G. Kresse, J. Furthmüller, 1996) [2]. The data is stored in the NIST dSpace repository (http://hdl.handle.net/11256/671).

Research paper thumbnail of Ti-V alloy phase diagram: DFT-based cluster approach

Bulletin of the American Physical Society, Mar 7, 2007

Research paper thumbnail of Ab initio-based interatomic potentials for body-centered cubic refractory metals

A fundamental understanding of transformation and deformation processes in the bcc refractory met... more A fundamental understanding of transformation and deformation processes in the bcc refractory metals (V, Nb, Ta, Mo, and W) is vital for designing new bcc-based commercial alloys with desired properties. Such an understanding is aided by computational methods capable of reaching length and time scales needed for meaningful simulations of phase transformations and extended defects responsible for plastic deformation. Classical interatomic potentials are indispensable for simulating such phenomena inaccessible to first-principles methods. We develop accurate and robust modified embedded-atom method (MEAM) potentials [1, 2] for the bcc metals by fitting the model parameters to accurate first-principles data. The potentials are applicable for studying mechanical and thermodynamic properties, yielding excellent agreement with both experiments and first-principles calculations. Supported by DOE-Basic Energy Sciences, Division of Materials Sciences (DE-FG02-99ER45795). Computational resources provided by OSC and NERSC.

Research paper thumbnail of Embedded-atom method potential for niobium

Aps Meeting Abstracts, Mar 1, 2010

Research paper thumbnail of Development of an Embedded-Atom Method Potential for Niobium

Aps Meeting Abstracts, Mar 1, 2009

Research paper thumbnail of Embedded Atom Method Potential for Titanium-Vanadium Alloys

Aps Meeting Abstracts, Mar 1, 2008

Research paper thumbnail of Force-matched embedded-atom method potential for niobium

Physical Review B, 2010

Large-scale simulations of plastic deformation and phase transformations in alloys require reliab... more Large-scale simulations of plastic deformation and phase transformations in alloys require reliable classical interatomic potentials. We construct an embedded-atom method potential for niobium as the first step in alloy potential development. Optimization of the potential parameters to a wellconverged set of density-functional theory (DFT) forces, energies, and stresses produces a reliable and transferable potential for molecular dynamics simulations. The potential accurately describes properties related to the fitting data, and also produces excellent results for quantities outside the fitting range. Structural and elastic properties, defect energetics, and thermal behavior compare well with DFT results and experimental data, e.g., DFT surface energies are reproduced with less than 4% error, generalized stacking-fault energies differ from DFT values by less than 15%, and the melting temperature is within 2% of the experimental value.

Research paper thumbnail of Grain-boundary free energy via thermodynamic integration

The Journal of Chemical Physics, 2006

In a previous publication by Lusk and Beale [Phys. Rev. E 69, 026117 (2004)], fluctuating cell (F... more In a previous publication by Lusk and Beale [Phys. Rev. E 69, 026117 (2004)], fluctuating cell (FC) theory was used to estimate the free energy of symmetric tilt grain boundaries in an assembly of nearly hard disks. The FC method is much faster than the more traditional thermodynamic integration, but the accuracy of the algorithm has not been assessed in association with persistent defect structures. This motivated the present work wherein the FC free energies are compared directly with the data obtained via thermodynamic integration from an Einstein crystal to an assembly of hard disks. This comparison is made over the range of possible misorientations for symmetric tilt boundaries and indicates that the FC method gives quantitatively accurate estimates for grain-boundary free energy. We also demsonstrate that the FC approximation is quantitatively accurate at determining the free-energy contribution of each particle whether in the bulk or the grain boundary. The FC calculation is about two orders of magnitude faster than a full thermodynamic integration. This approach may offer a numerically efficient means of estimating the free energy of persistent defect structures to greater accuracy than is afforded by the quasiharmonic and local harmonic approximations.

Research paper thumbnail of Ab initio based empirical potential used to study the mechanical properties of molybdenum

Density-functional theory energies, forces, and elastic constants determine the parametrization o... more Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for molybdenum. The accuracy and transferability of the potential are verified by comparison to experimental and density-functional data for point defects, phonons, thermal expansion, surface and stacking fault energies, and ideal shear strength. Searching the energy landscape predicted by the potential using a genetic algorithm verifies that it reproduces not only the correct bcc ground state of molybdenum but also all low-energy metastable phases. The potential is also applicable to the study of plastic deformation and used to compute energies, core structures, and Peierls stresses of screw and edge dislocations.